The ability to form categories that capture commonalities among objects and events in the environment is a critical aspect of adaptive functioning. Recent studies on categorization abilities of infants indicate that naming objects from the same category with a shared label facilitates the formation of object categories in infants as young as nine months of age. The current project extends this research by addressing three main issues in a series of studies with the visual familiarization/novelty-preference paradigm. The first aim is to track the developmental course of the influence of naming on categorization during the first year of life by comparing infants' response to word labels and nonlinguistic sounds in 6-, 9-, and 12-month-olds. At issue is whether word labels and nonlinguistic auditory stimuli both facilitate infants' object categorization relative to no sound early in development, and whether a general effect of sound later gives way to a more specific influence of word labels. The second aim is to evaluate whether the influence of word labels and nonlinguistic auditory stimuli on infants' object categorization results from infants' increased visual attention to category members in the presence of sound or from infants' detection of an association between category exemplars and a specific sound pattern. And the third aim is to examine the characteristics of word labels that lead to their facilitation of categorization at 6-, 9-, and 12-months of age. More specifically, is the influence of word labels on categorization related to the presentation of language in general, infant-directed language, or to the specific introduction of object labels (in English, count nouns in particular)? Results from the proposed studies will have implications for theories of language development regarding the basic processes underlying word teaming and address deep issues regarding the relationship between language and categorization in early development. Understanding how these basic processes develop normally will help to establish age-based standards for normal cognitive achievements and lay the foundation for understanding how such processes go awry, ultimately leading to the development of early assessment and intervention techniques for specific language impairments.